### Answers to Review Questions: Ch # 17 Dawn Of Modern Physics

XII BSEK ( Karachi Board)

Note:- For 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.7 ,17.12 see theory notes

Q.17.8 Why Compton Effect not observable with visible light?
Ans. In Compton effect ,x rays of wave length =1 Ao equivalent to energy=140 ev , were directed on the graphite block, where binding energies of bounded electrons are =100 ev .If visible light is used it possesses low frequency and these photons have energies =0.1 ev, this energy is too small to be given to loosely bound electrons to get them scattered.

Q.17.9 What phenomenon……………..related quantitatively?
 Evidences for wave Phenomenon Evidences for matter phenomenon Interference of light Black body radiation Diffraction of light Photo electric effect Polarization of light Compton effect Optical Doppler’s effect x ray production Prod. Of electromagnetic waves
Ans.

Q.17.10 In what way the …….  and protons?
Ans.
 Characteristics of particles of matter Characteristics of light (photons) 1.Non zero rest mass 1.Zero rest mass 2. They possess inertia 2.They consists of energy packets 3. Speed is always less than speed of light 3. They travel with the speed of light 4. They may be charged or uncharged 4. They are always neutral 5.They are guided by matter waves 5. No relation with the matter waves 6.E=1/2 mv2 6. E= hÎ½

Q.17.11 In the photo electric effect the energy……..Explain.
Ans. When radiation strikes a metal surface, it deposits its entire energy on some electron in the absorbing surface>if energy of the photon (E= hÎ½) exceeds the energy expend by the electron in work against the force binding it to the surface (Ï†) it will emitted with some energy. K.e < hÎ½

Q.17.13 with the help of ………. Of an atom.
Ans. A/c to de broglie hypothesis, an electron moving around nucleus is pictured as a kind of wave packet. An electron can circle a nucleus indefinitely without radiating energy provided that its orbit contains an integral number of de broglie wavelength.

### COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

COMMON COLLECTOR CONNECTION

In  this  configuration  the  input  is  applied  between the  base  and  the  collector and  the  output  is  taken  from  the  collector  and  the  emitter.  Here  the  collector  is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In  common  collector  configuration  the  input  current  is  the  base current  IB  and  the output current is the emitter current IE. The ratio of change in emitter current to the  change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test  circuit  for determining the  static characteristic  of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits.   To   measure   the   base   and   the   emitter   currents,   milli   ammeters   are connected in series with the base and the emitter circuits. Voltmeters are connected   across the input an…